For documents on the web you can add #page=<NUMBER> to the url.

\setupinteraction[state=start]

\starttext
\goto{Beginners 
manual}[url(http://pragma-ade.com/general/manuals/mp-cb-en.pdf\letterhash page=58)]
\stoptext

Wolfgang
> Hans van der Meer <mailto:havdmeer@ziggo.nl>
> 18. April 2018 um 21:12
> I have the following question about referencing.
>
> With \goto{typeset_the_text}[url(file://a_file_location_to_goto 
> <file:///a_file_location_to_goto>.pdf)] I can open a pdf from inside 
> the document that has been typeset. It would, however, be nice if I 
> could further specify on which page of the pdf to open. Is this 
> possible? Or is this a wish not to be fulfilled?
>
> dr. Hans van der Meer
>
>
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